The goal of this research is to gain a better understanding of adolescent physical activity and sedentary behavior by incorporating novel data about the social and physical environments in which adolescents spend their time. Ultimately, this research will identify leverage points within adolescent social networks that can be exploited to increase physical activity and decrease sedentary time. While recent research indicates that obesity may spread through social networks, we are unaware of any research that has attempted to investigate this issue with adolescent physical activity and sedentary behavior. The proposed study explores this phenomenon by collecting data from individual participants and up to six nominated peers, the school environment, and the physical environments of each participant and their nominated peers. Obtaining peer nomination data will allow us to examine the relationships between adolescent physical activity and sedentary behavior, their friends'behavior, the school environment and the neighborhood environments of the individual and their friends. The mediating role of individual-level psychosocial variables known to be associated with youth physical activity (e.g., self-efficacy, social support, enjoyment) will also be incorporated. This novel, multi-level approach bridges several disciplines (physical activity epidemiology, spatial mapping, and social networks) and has not been previously explored in the physical activity literature. The proposed study (Project P-EAT, Peers - Eating and Activity among Teens) expands on the already funded Project EAT-III in several ways. We will strategically increase the size of the Project EAT-III adolescent sample to increase the chance of obtaining data from nominated peers. A proposed sub-study will allow for additional in-depth data regarding possible mediating and moderating variables hypothesized to be related to the association between peer and individual PA and SED. Additional school-level data will be obtained to investigate the "spread" of student athletes into other non-sport clubs or organizations in the schools. Participants for Project P-EAT will be fully integrated into Project EAT-III and will provide all of the same data, thereby increasing the overall Project EAT-III sample size. Project P-EAT uses a cross-sectional design and, therefore, causal influences cannot be estimated. We will, however, obtain very rich baseline data that could be used in conjunction with data from planned future waves of Project EAT to examine the temporal associations between peers, environments, and individual PA and SED. This line of research will inform Dr. Sirard's future plans for an R01 application to develop, implement, and evaluate novel PA and SED interventions that use social networks (possibly popular students and central networks of friends within the school) to promote an active lifestyle and other healthy behaviors by shifting social norms at the school level. PUBLIC HEALTH RELEVANCE: Most U.S. adolescents are not meeting recommended levels of physical activity and are far exceeding recommended levels for screen media usage, helping to set the stage for excessive weight gain and other poor health outcomes. The proposed study (Project P-EAT, Peers - Eating and Activity among Teens) integrates different levels and sources of data to provide a more comprehensive view of the physical and social environments for adolescent physical activity and sedentary behavior. Achievement of our aims will inform the development of intervention efforts that act at the social network and school level to address the public health problem of adolescent inactivity.